In January, a Susaki official told The New York Times that the city was consulting a lawyer because it worried that Charando, the design company that owned a copyright for Chiitan, was profiting off its viral antics. That is a concern in Japan because the country allows its citizens to donate tax payments to municipalities of their choice — a potential windfall for a place with a flashy mascot.

Charando expressed remorse at the time that its mascot had caused problems for its hometown. But after the city filed a court case in February against Kleeblatt, Chiitan’s management company, in which it asked for the mascot to suspend its activities, Chiitan kept tweeting anyway.

This week, Chiitan’s Twitter accounts in several languages went dark without explanation or warning, Kleeblatt said in a statement on Friday. The real-life otter’s account was also suspended.

Kleeblatt said in an email that it had not posted anything prejudicial or malicious on the accounts, only “healthy” material. The mascot has also appeared on Instagram, where it has 1.6 million followers.

Ian Plunkett, a spokesman for Twitter, said in an email that the company does not comment on individual accounts out of privacy and security considerations.

Soumei Arisawa, a spokesman for the city of Susaki, said on Friday that the city had not contacted Twitter about Chiitan’s Twitter accounts, and that other characters managed by Kleeblatt had also been closed in recent days.

But Mr. Arisawa added that the city’s copyright dispute with Chiitan was continuing, and that the rogue mascot was created based on the design of Shinjokun, the city’s official mascot, who is also modeled on an otter. (Chiitan and Shinjokun share a designer but are based on different breeds of otter.)

“The city wants Chiitan to stop her activity,” he said. “Shinjokun has the copyright and Chiitan is created based on Shinjokun’s design.”

Chris Carlier, a British writer in Tokyo who runs the website and Twitter feed Mondo Mascots, said it struck him as unfair for Twitter to ban the accounts of a “children’s character” like Chiitan, given all the inflammatory information coursing through the platform.

But Twitter may have deemed it necessary to take action against the mascot, he said, if enough parents complained about the “anarchic” nature of its videos.

“I feel most sorry for the actual living otter Chiitan, who had already lost her job as Susaki City’s tourism ambassador, and has now had her Twitter account suspended,” Mr. Carlier said. “The world’s unluckiest otter!”

Chiitan is one of thousands of mascots, or “yuru-chara,” that have proliferated across Japan since the early 2000s. Most are sponsored by municipalities or companies and tend to promote specific cities or regions.

But as officials race to brand their municipalities with cuddly mascots, many young people have gravitated to edgier ones that are what they call “disturbingly cute,” said Jillian Rae Suter, a professor of informatics at Shizuoka University in Japan who has studied the yuru-chara phenomenon.

“Of course, Chiitan is really cute, but then he or she also does these subversive activities, so that might help with its popularity,” she said.

Chiitan is still not a household name within Japan, but its international profile grew last month when Mr. Oliver devoted a nearly 13-minute segment of his popular HBO show, “Last Week Tonight,” to the mascot and its feud with Susaki’s government.

Mr. Oliver called Chiitan “psychotic,” but praised its videos as “works of art” and its tweets as “virtuosic.” He also unveiled “Chiijohn,” a mascot version of himself that his show sent to Susaki to meet Shinjokun, the city’s official mascot.

Michelle Goldstein, a spokeswoman for HBO, said on Thursday that the show’s team had no comment on Chiitan’s Twitter suspension.

They were also visiting a Japanese-language Twitter account that Chiitan quietly opened on Thursday night. The account’s first post shows the mascot in signature naughty form: jumping over a wooden bar and crashing into a wall of metal cans.

“I’m going to post ‘Play house’ until the original account gets defrosted,” Chiitan said in the post.